Nowadays, soft drinks such as juice and alcoholic beverages such as beer are sold in the form of being filled in containers such as glass bottles or PET bottles, with a heat-shrinkable label indicating the content attached to the containers. As such a heat-shrinkable label, a polyester series heat-shrinkable film is mainly used, which has stiffness at room temperature, exhibits excellent heat resistance and solvent resistance, and has small natural shrinkage. However, the polyester series heat-shrinkable film has a drawback that it shrinks rapidly and therefore is likely to have shrinkage spots or wrinkles when fitted onto a container, compared with a polystyrene series heat-shrinkable film. Further, heat-shrinkable films are often perforated so that they can be easily removed from the container after use; however, the polyester series heat-shrinkable film cannot be cut well along the perforation and thus is sometimes hard to remove from the container.
On the other hand, the polystyrene series heat-shrinkable film which has excellent shrinkability at low temperature is also used as the heat-shrinkable label in many cases. However, the polystyrene series heat-shrinkable film has a drawback that it has a low degree of elongation at low temperature, therefore resulting in breaking of the label fitted onto the container when the container is dropped accidentally at a time of refrigeration. Additionally, the polystyrene series heat-shrinkable film has insufficient solvent resistance. Therefore, if an ordinary organic solvent-based gravure ink is used to print on the polystyrene series heat-shrinkage film, there occur: curling of the film; and blocking of the film after the printing or generation of odor of the organic solvent due to increase in the amount of the solvent remaining on the label.
As solutions to the above problems, there have been reported laminated films in a three-layer structure having two kinds of layers, wherein front and back layers made of a polyester series resin are respectively laminated on a middle layer made of a polystyrene series resin (see Patent Documents 1 to 3 for example). These three-layer laminated films having two kinds of layers adopt a configuration wherein an adhesive layer is formed between the front layer and the middle layer and between the back layer and the middle layer, for the purpose of preventing peeling between the front layer and the middle layer and between the back layer and the middle layer due to friction between the films during transportation, scratching of the film by a person's nail, or some other factors. For example, Patent Document 4 discloses a heat-shrinkable laminated film having a middle layer made of a polystyrene series resin and front and back layers made of a polyester series resin that are laminated with one another with an adhesive layer made of a polyolefin series resin disposed therebetween. However, when this heat-shrinkable laminated film is fitted onto a container, the front and back layers and the middle layer are peeled in the heat shrinking process, thus resulting in a poor appearance. Additionally, films having a polyester-based elastomer as an adhesive layer are disclosed as an approach to solving the peeling caused in the heat shrinking process or by a remaining solvent (see Patent Documents 6, 7, for example). These films are effective in terms of the adhesiveness; however, whitening occurs on the films when they are bent in the processing, namely the whitening on bending, resulting in difficulty in maintaining the design of the film in some cases.